A various kinds of methods for manufacturing a membrane electrode assembly (hereinafter referred to as MEA) are disclosed in patent documents, such as JPH3(1991)208260A, JPH5(1993)306345A, JPH8(1996)88007A and JPH11(1999)224679A. Such MEA for fuel cell has a structure, wherein an electrolyte membrane is sandwiched between two gas diffusion layers. In this circumstance, it is required that contact resistances on interfaces between the electrolyte membrane and the gas diffusion layers are reduced so as to improve an output characteristic of the fuel cell. Thus, a layered unit in which the electrolyte membrane is sandwiched between two gas diffusion layers is pressed in a thickness direction thereof by means of press dies, which are heated at above a predetermined temperature, of a pressing machine.
According to the known method for manufacturing the MEA, the contact resistances on the interfaces between the electrolyte membrane and two gas diffusion layers, which sandwich the electrolyte membrane, can be reduced so as to improve the output characteristics of the fuel cell. However, because the level of pressure applied to the layered unit is relatively large, the electrolyte membrane is pierced by elements (e.g. carbon fiber), which comprise the gas diffusion layer, as a result the electrolyte membrane may be damaged. Further, when the level of pressure becomes excessive, structures of the catalyst layers provided between the electrolyte membrane and two gas diffusion layers may be destroyed.
Thus, a need exists for providing a method for manufacturing the MEA, which can not only enhance the bondability on the interfaces between the electrolyte membrane and two gas diffusion layers which sandwich the electrolyte membrane but also prevent damages both on the electrolyte membrane and on the catalyst layer.